1. Field of the Invention
The present invention relates to a laser device and an optical signal amplifier using thereof, and especially to a laser device for generating a laser beam by supplying a pumping light to laser medium of a laser fiber and an optical signal amplifier for amplifying an optical signal using thereof.
2. Description of the Prior Art
Development of a practical laser device with a high power and low cost is expected in the optical communication industry and optical machining technology.
Among the promising technologies, it is known that an optical fiber laser oscillator or an optical waveguide type laser oscillator has an advantage in that the oscillation mode can be set single when such oscillators are designed and manufactured, by adjusting the core diameter and the refractive index difference between the core and a cladding. Such oscillators can also provide a high quality laser beam spatially and efficiently because the oscillators can present a high interaction between a laser medium and the beam by intensively confining the beam, and can present a long interaction in the fiber.
Here, one problem to be solved for realizing high power or high efficiency laser beam generation is to effectively introduce the pumping light into the addition area (usually a core portion) in which luminescence center such as laser activation ions or dye or the like is added or doped.
However, when the core diameter is set in accordance with a usual single mode wave guide condition, it is limited to the addition area in which the luminescence center is doped to have a diameter not larger than 10 and several xcexcm, which is too small to efficiently introduce the pumping light in general.
Therefore, a method is known using a device called a double cladding type fiber laser. The double cladding type fiber laser comprises a second cladding portion, outside a first cladding portion, which is made from a transparent substance having a lower refractive index than the first cladding portion. The pumping light introduced from the edge surface is confined within the first cladding portion and the core portion due to total reflection resulting from refractive index difference between the second cladding portion and the cladding portion, so that, as the confined pumping light passes through the addition area in which the luminescence center is added, the pumping light is progressively absorbed in the luminescence center, thereby to produce a high power of laser beam. (E. Snitzer, H. Po, F. Hakimi, R. Tumminelli, and B. C. McCllum, in Optical Fiber Sensors, vol.2 of 1988 OSA Technical Digest Series (Optical Society of America, Ishington D.C., 1988), paper PD5.).
However, in the double cladding type fiber laser, if the cross-sectional configuration of the inner cladding portion is circular, only the pumping light selectively passing through adjacent the addition area is effectively absorbed into the laser medium, and the absorption rate of the pumping light passing through other area is low. That is, absorption saturation occurs depending on modes.
Thus, effort is made to form the cross-sectional configuration of the inner cladding portion into rectangular. However, it is difficult in general to manufacture the fiber having other cross-sectional configurations other than circular, and such fiber tends to lack mechanical strength.
In order to resolve such problems, an optical fiber laser device (Japanese Laid-open Patent Application 10-135548) and a laser device (Japanese Laid-open Patent Application 10-190097) are proposed in which the pumping light is introduced to the addition area from lateral sides of the laser fiber.
When the pumping light is introduced from the lateral side into the addition area, the length of waveguide (L) is long compared to the diameter (d) of the addition area, resulting in L/d greater than 106, thus enabling to bring in a higher amount of excitation energy into the fiber or waveguide than the case where the pumping light is introduced from cross section side of the waveguide.
In the above optical fiber laser device and the laser device, the pumping light is transmitted in a manner to cross the fiber, so that it is necessary to provide a high optical quality construction with low losses at the gaps between the respective fibers. Therefore, such low loss construction is conventionally realized by embedding the fiber into an optical adhesive material.
However, when filling the gap with the optical adhesive material, it is necessary to use the optical adhesive material made of an organic substance, which is vulnerable to and easily damaged by the pumping light, that is, having low resistance against optical energy.
Further, the devices described above have a disadvantage in that efficiency for absorbing pumping light is low. This is so because, in the double cladding type fiber laser, pumping light of a mode which is able to pass through the area adjacent to the core portion where laser medium is doped is selectively absorbed, and pumping light of modes other than the pass through mode have constant and low absorption efficiencies.
Accordingly, it is an object of the present invention to provide a laser device and an optical signal amplifier using thereof which have a high optical energy resistance and are easy to manufacture.
It is also an object of the present invention to provide a laser device and an optical signal amplifier using thereof which have a high pumping light absorption efficiency.
The above object of the present invention is achieved by a laser device for generating a laser beam by supplying a pumping light to a laser medium contained in an optical fiber comprising an optical fiber having a core portion in which said laser medium is added and a cladding portion covering said core portion, a fluid medium having a refractive index substantially identical to said cladding portion at a wavelength of said pumping light, a pumping light reflecting portion having an inner space filled with said fluid medium and containing at least a part of said optical fiber thereby to confine said pumping light interiorly thereof, and a laser beam introducing port for introducing said pumping light into said pumping light reflecting portion, wherein said pumping light reflecting portion comprises a part of a passage for said fluid medium.
According to the present invention, the laser device comprises a pumping light reflecting portion installing a sufficiently long optical fiber and a fluid medium, and the fluid medium has a refractive index substantially identical to the outer periphery of the optical fiber, therefore, a laser device which is easy to manufacture and highly efficient can be realized.
Furthermore, the fluid medium flows so that deterioration of the medium due to heat generation can be suppressed thereby to realize a laser device having a high anti-optical power resistance.
The above object of the present invention is also achieved by an optical signal amplifier for amplifying an optical signal by supplying a pumping light to a laser medium contained in an optical fiber comprising an optical fiber having a core portion in which said laser medium is doped and a cladding portion covering said core portion, a fluid medium having a refractive index substantially identical to said cladding portion at a wavelength of said pumping light, a pumping light reflecting portion having an inner space filled with said fluid medium and containing at least a part of said optical fiber thereby to confine said pumping light interiorly thereof, and a laser beam introducing port for introducing said pumping light into said pumping light reflecting portion, wherein said pumping light reflecting portion comprises a part of a passage for said fluid medium.
According to the above invention, the optical signal amplifier comprises a pumping light reflecting portion installing a sufficiently long optical fiber and a fluid medium, and the fluid medium has a refractive index substantially identical to the outer periphery of the optical fiber, therefore, an optical signal amplifier which is easy to manufacture and highly efficient can be realized.
The above object of the present invention is also achieved by a laser device for performing a laser oscillation by using an optical fiber, said optical fiber having a core in which a laser medium is doped and a cladding covering said core, said laser device comprising an optical fiber bundle in which said optical fiber forming at least one optical path is bundled, a pumping light introducing portion for introducing pumping light for pumping said laser medium in said optical fiber, said pumping light introducing portion being bundled together with said optical fiber in said optical fiber bundle, a pumping light reflection portion covering at least a part of a side surface of said optical fiber bundle for repeatedly reflecting the pumping light so that said pumping light is absorbed in said laser medium, and a laser output portion for outputting a laser beam generated by said laser medium pumped by said pumping light.
According to the above invention, the laser device comprises a pumping light reflection portion covering the optical fiber bundle comprising an optical fiber, and a pumping light introducing portion for introducing pumping light for pumping the laser medium into the optical fiber bundle, thus introduced pumping light is repeatedly reflected at the pumping light reflection portion and is absorbed in the laser medium, therefore, the absorption rate of pumping light is increased to improve the oscillation efficiency.
The above object of the present invention is also achieved by an optical signal amplifier for amplifying an optical signal by using an optical fiber, said optical fiber having a core in which a laser medium is doped and a cladding covering said core, said optical signal amplifier comprising an optical fiber bundle in which said optical fiber forming at least one optical path is bundled, a pumping light introducing portion for introducing pumping light for pumping said laser medium in said optical fiber bundle, said pumping light introducing portion being bundled together with said optical fiber bundle, a pumping light reflection portion covering at least a part of a side surface of said optical fiber bundle for repeatedly reflecting the pumping light so that said pumping light is absorbed in said laser medium, and an output portion for outputting an optical signal amplified by said laser medium pumped by the pumping light.
Also, according to the above invention, the optical signal amplifier comprises a pumping light reflection portion covering the optical fiber bundle comprising an optical fiber, and a pumping light introducing portion for introducing pumping light for pumping the laser medium into the optical fiber bundle, thus introduced pumping light is repeatedly reflected at the pumping light reflection portion and is absorbed in the laser medium, therefore, the absorption rate of the pumping light is increased to improve the amplifying efficiency.